Commonly assignee U.S. Pat. No. 4,326,803, issued Apr. 27, 1982 and commonly assigned U.S. Pat. No. 4,674,881, issued Jun. 23, 1987 disclose thin film laser gyroscopes, also known as micro-optic gyroscopes (MOGs). The MOG includes a thin-film passive resonator waveguide that provides a closed, substantially circular propagation path for optical signals. The resonator waveguide is fabricated upon or within a surface of a substrate and is typically 1-2 microns in depth, 5-10 microns in width and has an overall diameter of approximately 10 centimeters.
A finesse of the resonator is represented by (q) and is a measure of the quality factor of the resonator. Finesse may be determined in accordance with the expression: EQU q=FSR/L,
where FSR is the free spectral range of the resonator and L is the line width between adjacent half-power points on the resonance curve.
A high finesse resonator is realized only if optical losses are maintained below a few percent. This results in a requirement that a dielectric waveguide have a distributed loss of approximately 10.sup.-2 to 10.sup.-3 dB/cm. For a 10 cm ring, guide loss is thus 0.3 dB to 0.03 dB. Using 5.times.10.sup.-3 dB/cm as an example, waveguide loss is 0.16 dB or 3.7%. As a result, and assuming one percent input-output coupling, the finesse is approximately 100.
However, a waveguide loss of 5.times.10.sup.-3 dB/cm is difficult to achieve using conventional passive resonator waveguides.
In U.S. Pat. No. 3,974,454, issued Aug. 10, 1976 and entitled "Laser Amplifiers" B. Sturel describes an improvement realized in a neodymium glass optical amplifier by shaping it in a particular way such that diffraction effects are minimized.
In U.S. Pat. No. 4,676,583, issued Jun. 30, 1987 and entitled "Adscititious Resonator" J. W. Hicks, Jr. describes fiber optic resonators and an adscititious cavity doped with a gain material such as neodymium (Nd). However, this discussion is made in the context of filtering out, or absorbing, light of a particular wavelength from a fiber optic data bus.
It is thus an object of the invention to provide a micro-optic gyroscope having a high finesse.
It is another object of the invention to provide a micro-optic gyroscope having an optical path with a predetermined amount of regenerative gain.
It is a further object of the invention to provide a micro-optic gyroscope having an optical path comprised of Nd-doped glass for providing regenerative optical gain.